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Whenever I check on violin-learning-related sites, they usually begin talking about the quality of a violin. The strings, the species of woods...
... the species of wood. Ebony? Maple? Rosewood? I think I understand how important the string quality might be, but I don't really see why should I even care for the type of woods used.
Since everyone keeps talking about it, I wonder: does the kind of wood used in a violin matter in any way?
The wood type in any stringed instrument matters a great deal, especially on acoustic instruments. Some parts of the violin contribute more to the overall tone quality than others, but all the parts make a difference.
A stringed instrument is a case study in engineering trade-offs. After all, how does a violin produce its sound? To begin with, note that the body of a violin is basically an empty box full of air. The sound you hear a violin producing is the result of that air vibrating and escaping out the F-holes of the instrument. How does this happen? Drawing the bow across a string causes that string to vibrate. The vibration of the string causes the bridge to vibrate, which in turn causes the top of the violin to vibrate. The vibration of the top of the violin is passed through the sound post to the back of the violin, and the two parts---the top and the back---now both vibrate. This causes the air trapped between them to vibrate and get pumped out of the F-holes into the surrounding air, and that vibration is what you hear.
So, you want the wood of the violin to transfer the vibrations of the strings to the box of air as efficiently as possible in order to produce the most sound, and so you want the wood of the instrument to be light and resonant. Maybe a nice light balsa would do the trick?
But no luck, because of the inherent engineering challenge: While you want the violin to be as light and resonant as possible, it also has to withstand the significant string tension of four strings pulling on it and trying to fold it up. If the wood is too light and weak, the violin will collapse like a cardboard box, which obviously is no good. If you build the violin to be too heavy and sturdy, though, it will absorb and reflect the strings' vibrations rather than passing them along to the air. It's a tough problem to solve.
So to build a violin, you want wood that has all these qualities: it has to be light, resonant, strong, stiff, and sturdy. These are difficult qualities to find all in one species of wood, but a few kinds have proven to be effective: cedar, spruce, mahogany, walnut, maple, etc. All of these woods work well for acoustic stringed instruments, but they each behave slightly differently when transferring the strings' vibrations into the body of the instrument.
The point is: The entire acoustic mechanics of a violin (or any stringed instrument) completely depend on the ways in which the various pieces of wood transfer the vibrational energy of the strings into the box of air. Different kinds of wood resonate differently and thus transfer that energy differently, and as such, the kind and quality of the wood of a violin makes all the difference in its sound.
I would also add that the species of woods used is only part of the equation. The quality of each piece of wood makes a huge difference. A builder will go through many pieces of maple or spruce from a lumberyard to select only the logs or planks of wood with the highest quality for making instruments. They will reject the vast majority of the wood as only suitable for furniture or chopsticks (seriously).
I know little about what criteria are used, but I understand that a musical instrument maker will only select and purchase specific pieces of lumber that come from trees where the growth of the wood was extremely straight (not twisted or gnarled) and of a certain density and even pattern of grain, because only these are likely to result in an instrument that resonates well. We call these "tonewoods".
Wood selected for instruments must come from extremely old trees, because only in the oldest trees do the cells in the wood reach the required density to make a resonant instrument. (The age of the tree needed for good tonewood varies with the species.) The best cut wood that is selected is then usually "seasoned", or left to dry in controlled conditions, for many months, sometimes for decades, before it is used to build an instrument. This is so the wood can dry out and achieve a stable consistency suitable for carving into an instrument.
Consequently, good tonewood is rare and expensive. Throughout the past century, the supply of quality tonewoods around the world has become extremely constrained due to over-harvesting, and certain species of wood used for instruments have even been put on endangered species lists and have become practically unavailable for building new musical instruments.
The result of this is that the price of a violin or guitar reflects whether or not it is made from expensive and rare old-growth tonewood-quality spruce and maple, or whether it is made from inferior and cheap spruce and maple. Of course the skill of the people who make the instrument is also extremely important.
In his answer Alex mentions that "you want the violin to be as light and resonant as possible, it also has to withstand the significant string tension". In the book Materials Selection in Mechanical Design by Michael F. Ashby there is a table showing the relative strength and density of different materials:
This is then tailored to violin use by Dr Claire Barlow in her paper "Materials Selection for Musical Instruments" in the Proceedings of the Institute of Acoustics 19(5) pages 69−78:
(N.B. This is not the exact diagram from the paper, but one supplied by Barlow with the 'solid wood' point correctly plotted at 35GPa, as stated in the text of the paper.)
I encountered this figure in a fascinating introduction to the science and engineering of violin design given locally by Professor Jim Woodhouse from the University of Cambridge's Dynamics & Vibration Research Group. After his fabulous talk he took questions. I asked if carbon fibre will make a better material for violins. He dug out Barlow's diagram and pointed out that the island of materials sitting in the top left quadrant are the best; and they are woods! If the axes measured were the only ones that mattered then the best violins would be made from balsa wood (!) though clearly that material has other problems that prevent its use in violin making. (Jim mentioned that there is someone experimenting with balsa wood violins, Douglas Martin perhaps.)
Looking on Google Scholar at the papers which cite Barlow there are others we may want to read. These two look particularly interesting:
It's also worth noting that a lot of workmanship goes into producing the balance between strength and pliability of the material. If you use CNC techniques for producing important string instrument parts, particularly the top, then you are not working with the grain and the strengths of the material. In addition, cheap wood is less stable. The result is that such a junk violin has to have its sounding parts milled considerably thicker than a hand-made violin.
Adding to that the basically inferior quality of the used woods, you can expect quite bad resonance, and you also can expect parts to warp over time. A roommate once had a $30 guitar bought few years ago, and the fretboard was already so warped that there was a range of about a fifth that was not playable at all because it would register with a higher fret than fingered.
Really, you cannot fathom just how bad instruments can be until having tried some of those gimmicks few years after they left factory. It's possible that they work for a limited time right after production if you don't expect useful sound quality.
The problem of getting proper wood, and the problem of machines not being to able to work with the properties of the wood mean that mass-manufactured "Antonius Stradivarius" knockoff violins from the beginning of the 20th century near the Bohemian woods, if in reasonable shape, are quite competitive.
"Manufactured" meant hand-made, and even when using a ridiculously small amount of time for improving the instrument, the factory workers had a job to lose and improved over time. It's similar with the mass-manufactured bellows instruments of that time: "Alfred Arnold" Bandoneons were cheaper than regular accordions, and are nowadays desperately sought after and painstakingly restored for Argentinian Tango.
